A design method for drawing metal pipe fittings based on a fixed mandrel conical die

Abstract

The present invention belongs to the technical field of metal tube conical die drawing, and specifically discloses a design method for drawing metal pipe fittings based on a fixed mandrel conical die. The design method of the present invention first obtains the yield strength and flow stress model of the metal pipe fitting drawing. Based on the known wall thickness of the incoming pipe fitting, the outer diameter and wall thickness of the finished pipe, the drawing rate, the drawing temperature and the flow stress model, using the outer diameter of the incoming pipe fitting as a variable, the total drawing stress is calculated. In the calculation, the optimal compression angle value is determined on the condition that the minimum value of the drawing stress is obtained, and the calculation is terminated on the condition that the maximum drawing tightness is obtained. Finally, the key process parameters such as the maximum outer diameter of the incoming metal pipe fitting and the optimal compression angle of the drawing hole are determined to achieve process optimization. The design method of the present invention improves the process design efficiency and reduces the trial-and-error cost of the process on the production site.

Description

Technical Field

[0001] The invention belongs to the technical field of metal tube tapered die drawing, and in particular relates to a design method for drawing a metal tube based on a fixed mandrel tapered die. Background Art

[0002] The metal pipe deformation process by drawing with a fixed mandrel cone die is one of the methods of metal plastic forming. It can not only reduce the diameter and wall of the metal pipe to achieve the target product size, but also refine the metal material grains and improve the mechanical properties. Therefore, it is widely used in the drawing production of metal pipes. In this drawing deformation process, maximizing the deformation amount of each pass can make the metal grains finer, the structure more uniform, and the surface quality better, but it also brings the risk of instability or even breaking of the pipe drawing. Therefore, how to maximize the drawing deformation amount of each pass while avoiding excessive drawing force through reasonable process design has always been a technical problem that has plagued the on-site production of enterprises. At present, the use of finite element simulation technology has made certain progress in the study of the deformation law of the drawing process. Although it can help to design the drawing process to a certain extent, its simulation calculation is large and time-consuming, and it cannot meet the real-time and high-efficiency requirements of process formulation and optimization on the production line. How to research and develop a method that can scientifically, reasonably, quickly and efficiently realize the design and calculation of the drawing process, so as to maximize the deformation of the pass in the fixed mandrel conical die drawing process while avoiding the instability of the drawing process has become an urgent technical need. Summary of the invention

[0003] In view of the above-mentioned prior art problems involving maximizing the deformation amount per pass and avoiding instability of the drawing process during the drawing process with a fixed mandrel conical die, as well as the problems of design and calculation, the present invention will provide a design method for drawing metal pipes based on a fixed mandrel conical die.

[0004] To achieve the above purpose, the following technical solutions are specifically included:

[0005] A design method for drawing a metal pipe based on a fixed mandrel tapered die comprises the following steps:

[0006] (1) Obtain the yield strength of metal pipes through tensile tests ;

[0007] (2) Obtain stress-strain curves of multiple groups of metal pipe fittings through Gleeble test, and obtain the rheological stress model of metal pipe fittings through the stress-strain curves of multiple groups of metal pipe fittings;

[0008] (3) Obtain processing deformation temperature T and drawing exit line speed , Wall thickness of finished pipe , Outer diameter of finished pipe , the wall thickness of the incoming metal pipe fitting , the friction coefficient between the metal pipe fitting and the inner hole wall of the die and the friction coefficient between the metal pipe fitting and the mandrel ;

[0009] (4) Preset a fixed mandrel conical die, draw the incoming metal pipe fitting to obtain a finished pipe, divide the deformation zone of the metal pipe fitting during the drawing process into a diameter reduction zone and a wall thickness reduction zone, and based on the rheological stress model of the metal pipe fitting described in step (2), the parameters obtained in step (3), and the calculation formula in the energy method, with the outer diameter of the incoming metal pipe fitting and the compression angle of the drawing hole as variables, iteratively calculate the average drawing stress at the outlet end face of the drawn pipe fitting. The termination condition for the iterative calculation is:

[0010]

[0011] In the formula, is the error value; after terminating the calculation, the corresponding designed , are obtained.

[0012] The maximization strategy of the pass deformation amount of the metal pipe fitting in the present invention is to pursue the maximization of the outer diameter of the incoming metal pipe fitting under the condition that the wall thickness of the incoming metal pipe fitting is fixed. The present invention combines the design and calculation of the outer diameter and wall thickness of the incoming metal pipe fitting and the finished pipe, the optimized compression angle of the drawing hole, and the maximum drawing tension degree, so that the pipe fitting outside the drawing die is in a reasonable maximum drawing tension mechanical state, that is, when the average drawing stress at the outlet end face of the drawn pipe fitting is close to 0.75 times the yield strength of the metal pipe fitting, the iterative calculation is terminated, while achieving the maximization of the pass deformation amount of the drawing process and ensuring the process safety and stability, that is: the drawn workpiece does not break, nor enter the plastic state outside the drawing die. The present invention can improve the efficiency of process design, effectively reduce the process trial-and-error cost, and improve the production efficiency.

[0013] In the design method of the present invention, first, the yield strength and the flow stress model of the metal pipe fitting drawing are obtained. The outer diameter of the incoming metal pipe fitting is preset as a fixed value. Then, taking the drawing hole compression angle as a variable, the optimized drawing hole compression angle is obtained through iterative calculation using the energy method calculation formula. Based on the known optimized drawing hole compression angle, the outer diameter and wall thickness of the finished pipe, the drawing rate, the drawing temperature, and the flow stress model, taking the outer diameter of the incoming metal pipe fitting as a variable, the real-time theoretical drawing stress during drawing is iteratively calculated. During the iterative calculation, the real-time theoretical drawing stress is made close to 0.75 times the yield strength of the metal pipe fitting drawing, so as to include the maximum tightening degree mechanical state of the drawn metal pipe fitting into the calculation scope. After the iterative calculation is terminated, the corresponding outer diameter of the incoming metal pipe fitting and other process parameters can be determined. The design method of the present invention comprehensively applies the modeling technology based on metal mechanics test data and material constitutive models, the analytical calculation based on the principle of plastic mechanics, and the computer programming iterative solution technology, improves the process design efficiency, reduces the trial-and-error cost of the process at the production site, and thus creates economic benefits.

[0014] Preferably, in step (1), during the tensile test process, a plurality of tensile pause points are set so that the yield strength of the metal pipe fitting is the yield strength of the metal pipe fitting with the cumulative work hardening effect.

[0015] Preferably, in step (2), the flow stress model of the metal pipe fitting is the Johnson-Cook flow stress model. Preferably, in step (4), the calculation formula in the energy method includes the following calculation formula:

[0016]

[0017] In the formula,

[0018] is the work done by the drawing force at the drawing outlet corresponding to the unit volume, and its calculation formula is:

[0019]

[0020] In the formula,

[0021] is the average drawing stress at the outlet end face of the drawn pipe fitting;

[0022] is the metal flow during drawing corresponding to the length of the pipe fitting after drawing;

[0023] is the metal flow during drawing corresponding to the length of the pipe fitting before drawing;

[0024] is the ideal unit volume strain energy of the reducing zone, and its calculation formula is:

[0025]

[0026] In the formula,

[0027] is the average flow stress corresponding to the reducing deformation zone;

[0028] is the equivalent strain value that occurs in the metal pipe fitting within the reducing deformation zone, and its calculation formula is:

[0029]

[0030] In the formula,

[0031]

[0032]

[0033]

[0034] Substitute the above into the flow stress model of the metal pipe fitting described in step (2) to calculate and obtain the average flow stress in the drawing and reducing zone. And during the calculation process, take the approximate value calculation formula of the equivalent strain degree as:

[0035]

[0036] The calculation formula of the equivalent strain rate is:

[0037]

[0038] In the formula, t is the deformation time for the metal to pass through the deformation zone, and its calculation formula is:

[0039]

[0040] In the formula,

[0041] is the inlet linear velocity of the metal pipe fitting; is the instantaneous linear velocity of the metal pipe fitting when it enters the wall thickness reducing zone; , The values of are calculated according to the law of conservation of metal volume on the premise of knowing the drawing outlet linear velocity

[0042] is the ideal unit volume strain energy of the wall thickness reducing zone, and its calculation formula is:

[0043]

[0044] In the formula,

[0045] is the average flow stress corresponding to the wall-thinning deformation zone;

[0046] is the equivalent strain value occurring in the pipe fitting within the wall-thinning deformation zone, and its calculation formula is:

[0047]

[0048] In the formula,

[0049]

[0050]

[0051]

[0052] Substitute the above into the flow stress model of the metal pipe fitting described in step (2) to calculate and obtain the average flow stress in the drawing wall-thinning zone; during the calculation process, the approximate value calculation formula for the equivalent strain degree is:

[0053]

[0054] The equivalent strain rate has the following calculation formula:

[0055]

[0056] In the formula, t is the deformation time for the metal to pass through the deformation zone, and its calculation formula is:

[0057]

[0058] In the formula,

[0059] is the drawing outlet linear velocity of the metal pipe fitting, is the instantaneous linear velocity of the metal pipe fitting at the entrance of the wall-thinning zone, , The values of are calculated according to the law of conservation of metal volume on the premise of knowing the drawing outlet linear velocity

[0060] is the shear strain energy per unit volume in the deformation zone, and its calculation formula is:

[0061]

[0062] In the formula, is the compression angle of the drawing hole;

[0063] is the work done by friction per unit volume in the deformation zone, and its calculation formula is:

[0064]

[0065] In the formula,

[0066] is the friction coefficient between the metal pipe fitting and the inner hole wall of the die;

[0067] is the friction coefficient between the metal pipe fitting and the mandrel;

[0068] is the radial component of the pressure of the die on the metal pipe fitting in the diameter reduction zone;

[0069] is the radial component of the pressure of the die on the metal pipe fitting in the wall thickness reduction zone;

[0070] is the pressure of the mandrel on the inner wall of the metal pipe fitting in the wall thickness reduction zone;

[0071] is the work length of the metal per unit volume flow to overcome friction in the diameter reduction zone;

[0072] is the work length of the metal per unit volume flow to overcome friction in the wall thickness reduction zone.

[0073] Preferably, in step (3), the is 0.5 - 4 mm.

[0074] Preferably, in step (3), the is 20 - 40 mm.

[0075] Preferably, in step (3), the is 0.5 - 4 mm.

[0076] Preferably, in step (3), the is 400 - 800 mm / s.

[0077] Preferably, in step (3), the is 15 - 30 °C.

[0078] Preferably, in step (4), the is 30 - 80 mm.

[0079] Preferably, in step (4), the is 8 - 20°.

[0080] Preferably, in step (4), the <1%, more preferably <0.1%.

[0081] The closer the error value is to 0, the average drawing stress at the outlet end face of the drawn pipe fitting is closer to 0.75 times the yield strength of the metal pipe fitting , and the drawing instability of the pipe fitting caused by large - amplitude deformation in a single pass can be avoided.

[0082] Compared with the prior art, the present invention has the following beneficial effects: (1) The design method of the present invention is based on scientific engineering calculations for process design. While obtaining the maximum deformation amount of the fixed - mandrel conical die drawing pass, it can avoid the drawing instability of the pipe fitting caused by large - amplitude deformation in a single pass; (2) The design method of the present invention, due to the comprehensive application of the modeling technology based on metal mechanics test data and material constitutive models, the analytical calculation based on the principles of plasticity mechanics, and the computer programming iterative solution technology, improves the process design efficiency, reduces the process trial - and - error cost at the production site, and thus creates economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0083] Figure 1 is the calculation flow chart in the embodiment of the present invention.

[0084] Figure 2 is the structural schematic diagram of the drawing deformation zone of the fixed - mandrel conical die in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0085] To better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described through specific embodiments. The test methods used in the embodiments and / or comparative examples are all conventional methods unless otherwise specified; the materials, reagents, etc. used are all commercially available unless otherwise specified.

[0086] In the present invention, the units of the various parameters involved are as follows: , , , The units of are all mm; The unit of is mm / s; the unit of T is °C, , The units of are °, and the radian unit rad is used in the calculation; , The units of are all MPa.

[0087] Example 1

[0088] A design method for drawing metal pipe fittings based on a fixed mandrel conical die, the calculation flow chart of which is as shown in Figure 1 the figure, and the schematic diagram of the die structure is as shown in the appendix Figure 2 figure, and specifically includes the following steps:

[0089] (1) Obtain the metal yield strength: The yield strength of the metal pipe fitting considering work hardening is obtained through the tensile test of the metal pipe fitting specific value.

[0090] For example, the as-cast drawn specimen is used as the tensile sample without work hardening, the tensile specimen obtained after the equivalent strain degree accumulates to 0.4 after cold drawing from the as-cast specimen is regarded as the sample after medium work hardening, and the tensile specimen obtained after the equivalent strain degree accumulates to 0.85 after cold drawing from the as-cast specimen is regarded as the sample after high work hardening. The corresponding metal yield strength values are detected by drawing the samples respectively, so that the actual metal yield strength in the drawing deformation can be estimated by the interpolation method .

[0091] (2) Obtain the JC model coefficients: Apply the Gleeble testing machine to conduct tensile tests under different temperatures and strain rates, and use the deformation resistance model to fit the stress-strain curve obtained from the test to obtain the material constants in the deformation resistance model of the metal for subsequent calculations.

[0092] Taking the Johnson-Cook model as the deformation resistance model as an example, use the following formula:

[0093]

[0094] In the formula,

[0095] is the average flow stress in the drawing deformation zone;

[0096] A, B, C, n, and m are all material constants;

[0097] is the equivalent strain degree;

[0098] is the dimensionless equivalent strain rate, and the calculation formula is:

[0099]

[0100] In the formula,

[0101] is the equivalent strain rate;

[0102] is the equivalent strain rate reference value;

[0103] is the dimensionless temperature coefficient, and its calculation formula is:

[0104]

[0105] In the formula, , , are the average deformation temperature, the reference room temperature, and the material melting point temperature of the metal material undergoing current processing deformation, respectively.

[0106] (3) Obtain the working condition parameters: Preset and determine the processing deformation temperature T, the drawing exit linear velocity , the wall thickness of the finished pipe , and the wall thickness of the incoming metal pipe fitting .

[0107] (4) Obtain the die-related parameters: Preset and determine the diameter of the finished pipe (including the outer diameter of the finished pipe), the mandrel diameter, the friction coefficient between the pipe fitting and the inner hole wall of the die, and the friction coefficient between the pipe fitting and the mandrel.

[0108] (5) Preset the outer diameter of the incoming metal pipe fitting as , the wall thickness of the incoming metal pipe fitting as , the outer diameter of the finished pipe as , and the wall thickness of the finished pipe as ; During the drawing process, the drawing exit linear velocity , the processing deformation temperature is T, the average drawing stress (abbreviated as drawing stress) at the exit end face of the drawn pipe fitting is , and the drawing hole compression angle is ;

[0109] (5-1) During the drawing process, the total length of the deformation zone of the metal pipe fitting can be determined by the specifications of the incoming pipe fitting and the geometric parameters of the drawing die, and it is divided into a diameter reduction zone and a wall thickness reduction zone.

[0110] The method for determining the length of the diameter reduction zone is as follows: According to the principle of elementary plastic mechanics, program and iteratively calculate the wall thickness change of the pipe fitting during the diameter reduction deformation in the diameter reduction zone, that is, calculate the real-time outer diameter and wall thickness of the pipe fitting when moving in the diameter reduction zone. When the real-time wall thickness can fill the gap value between the die wall and the mandrel, it is determined that the position is the end point of the diameter reduction zone, and the subsequent region with wall thickness thinning in the deformation zone is the wall thickness reduction zone. Given the outer diameter and wall thickness of the pipe fitting at the end position of the diameter reduction zone, the and of the pipe before drawing and the and of the pipe fitting after drawing can be combined.Values. According to the elementary plastic theory of pipe deformation, the compressive stress on the outer surface of the pipe in the reducing zone and the compressive stress values on the inner and outer surfaces of the pipe fitting in the wall-thinning zone can be calculated. Thus, according to the principle of the energy method, the ideal work of the drawing deformation work can be conveniently calculated. Based on the ideal work, the average flow stress value of the metal in the deformation zone can be estimated, and further, the friction work and shear work parts can be calculated. The specific relationships are as follows:

[0111] Average drawing stress at the outlet end face of the drawn pipe fitting It can be calculated according to the energy method:

[0112]

[0113] In the formula,

[0114] is the work done by the drawing force per unit volume corresponding to the outlet drawing, and its calculation formula is:

[0115]

[0116] In the formula, is the average drawing stress at the outlet end face of the drawn pipe fitting, is the metal flow rate during drawing corresponding to the length of the pipe fitting after drawing, is the metal flow rate during drawing corresponding to the length of the pipe fitting before drawing;

[0117] is the ideal strain energy per unit volume in the reducing zone, and its calculation formula is:

[0118]

[0119] In the formula,

[0120] is the average flow stress corresponding to the reducing deformation zone;

[0121] is the equivalent strain value occurring in the pipe fitting in the reducing deformation zone, and its estimation calculation formula is:

[0122]

[0123] In the formula,

[0124]

[0125]

[0126]

[0127] Substitute the above strain degree and strain rate values into the flow stress model, and the average flow stress in the drawing and reducing zone can be calculated and obtained. .

[0128] During the calculation process, the approximate value calculation formula for the equivalent strain degree is:

[0129]

[0130] The calculation formula for the equivalent strain rate is:

[0131]

[0132] In the formula, t is the deformation time of the metal passing through the deformation zone, and its calculation formula is:

[0133]

[0134] In the formula,

[0135] is the inlet linear velocity of the metal tube;

[0136] is the instantaneous linear velocity of the metal tube at the entrance of the wall-reducing zone, and its value can be calculated according to the law of constant metal volume on the premise of knowing the drawing outlet velocity of the metal tube.

[0137] is the ideal unit volume strain energy of the wall-reducing zone, and its calculation formula is:

[0138]

[0139] In the formula

[0140] is the average flow stress corresponding to the wall-reducing deformation zone;

[0141] is the value of the equivalent strain degree occurring in the pipe fitting in the wall-reducing deformation zone, and its estimation calculation formula is:

[0142]

[0143] In the formula,

[0144]

[0145]

[0146]

[0147] Substitute the above strain level and strain rate values into the flow stress model, and the average flow stress in the wall-reducing drawing zone can be calculated and obtained. ; During the calculation process, the approximate value calculation formula of the equivalent strain level is:

[0148]

[0149] The equivalent strain rate is calculated as:

[0150]

[0151] In the formula, t is the deformation time of the metal passing through the deformation zone, and its calculation formula is:

[0152]

[0153] In the formula,

[0154] is the drawing outlet linear velocity of the metal tube;

[0155] is the instantaneous linear velocity of the metal tube at the entrance of the wall-reducing zone.

[0156] is the shear strain energy per unit volume in the deformation zone, and its calculation formula is:

[0157]

[0158] is the work done by friction per unit volume in the deformation zone, and its calculation formula is:

[0159]

[0160] In the formula,

[0161] is the friction coefficient between the pipe fitting and the inner hole wall of the die;

[0162] is the friction coefficient between the pipe fitting and the mandrel;

[0163] is the radial component of the pressure of the die on the pipe fitting in the diameter-reducing zone;

[0164] is the radial component of the pressure of the die on the pipe fitting in the wall-reducing zone;

[0165] is the pressure of the mandrel on the inner wall of the pipe fitting in the wall-reducing zone (here, 、 、 The calculation method can be obtained by conventional methods. Specifically, for example, the theoretical calculation method of Toyohiko Okamoto recorded on page 163 of "Theory of Pipe Continuous Rolling" can be referred to;

[0166] is the length of the friction work done by the metal with a unit volume flow rate in overcoming friction in the reducing zone;

[0167] is the length of the friction work done by the metal with a unit volume flow rate in overcoming friction in the wall thickness reduction zone.

[0168] (5 - 3) As shown in the above-mentioned shear strain energy and the friction work value in the estimation formula, the compression angle of the drawing die in the drawing process has an opposite effect on the friction work and the shear deformation work. Therefore, based on the principle of the energy method, through the trial-and-error method iteration calculation of computer programming, using the outer diameter of the incoming metal pipe fitting and the compression angle of the drawing die as variables, an iteration calculation is performed to obtain a compression angle as the optimal compression angle value , and the angle value of this compression angle makes the average drawing stress value at the outlet end face of the drawn pipe fitting reach the minimum average drawing stress value of the drawn pipe fitting. Then, the minimum average drawing stress value of the drawn pipe fitting is compared with 0.75 times of ; when is close to 0.75 times of , and there is only a slight deviation between the obtained real-time tightening degree and the reasonable maximum tightening degree allowed by the process design, the iteration calculation terminates. The condition for the termination of the iteration calculation is:

[0169]

[0170] In the formula, takes a value close to 0.

[0171] The specific process is as follows:

[0172] S1: In steps (3) and (4), the situation of the incoming metal pipe fitting and the finished pipe has been determined. The outer diameter of the incoming metal pipe fitting is unknown. Therefore, a value is preset for the outer diameter of the incoming metal pipe fitting, and a value is preset for the compression angle of the drawing die;

[0173] S2: Calculate the reduction in diameter and increase in thickness to determine the reducing zone and the wall thickness reduction zone, and calculate the shear stress corresponding to the reducing zone based on the above formula (including the shear strain energy ), and the shear stress corresponding to the drawing stress and the wall thickness reduction zone (including the shear strain energy ), and the drawing stress; then calculate the total real-time drawing stress on the pipe at the outlet of the drawing hole ;

[0174] S3: Then reset the compression angle of the drawing hole to a new value, recalculate the diameter reduction and wall thickness increase to determine the diameter reduction zone and the wall thickness reduction zone, and recalculate the shear stress corresponding to the diameter reduction zone (including the shear strain energy ), and the drawing stress, and the shear stress corresponding to the wall thickness reduction zone (including the shear strain energy ); then recalculate the total real-time drawing stress on the pipe at the outlet of the drawing hole ;

[0175] S4: Iteratively calculate the above process to obtain a compression angle as the optimal compression angle value , and this compression angle value makes the average drawing stress value at the outlet end face of the drawn pipe fitting reach the minimum average drawing stress value at the outlet end face of the drawn pipe fitting , and then compare the minimum average drawing stress value at the outlet end face of the drawn pipe fitting with 0.75 times of ; when is not yet close to 0.75 times of , that is, when the above iterative calculation termination condition cannot be satisfied, iterate the process of steps S1 - S4 until the iterative calculation terminates.

[0176] S5: Terminate the calculation and organize to obtain the corresponding , , , , , T, , .

[0177] The maximization strategy of the pass deformation amount of the metal pipe fitting in this embodiment is to pursue the maximization of the outer diameter of the incoming metal pipe fitting under the condition that the wall thickness of the incoming metal pipe fitting is fixed.

[0178] The design method of this embodiment is applied to the process table and working conditions of drawing oxygen-free copper copper pipes with a fixed mandrel conical die as shown in Table 1 below.

[0179] Table 1

[0180]

[0181] Comparative Example 1

[0182] The process table and the current working conditions for designing the drawing of oxygen-free copper copper tubes with a conical die by the traditional empirical method are shown in Table 2 below.

[0183] Table 2

[0184]

[0185] Through production verification, production can be organized normally according to Process Table 1 of the present invention. By comparing the process data in Table 1 and Table 2, the effectiveness of the process design method of the present invention can be verified. The design method of the present invention not only solves the problem of frequent drawing instability in the original process, but also increases the pass variable reduction rate of the fixed mandrel conical die by about 9.5% (the increment of the pass variable reduction rate %=(43.2 - 30) / 43.2-(38 - 30) / 38), achieving the maximization of the outer diameter or wall thickness of the incoming material.

[0186] The present invention ensures the safety and stability of the process by using an optimized compression angle, maximum deformation amount, and reasonable maximum tension degree in the drawing process through a process design method, so that the production potential of the production equipment can be maximally exerted, the process organization cost can be reduced, the production efficiency can be improved, and the process technology level can be improved and economic benefits can be created in actual production.

[0187] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A design method for drawing metal pipe fittings based on a fixed mandrel conical die, characterized in that, It includes the following steps: (1)Obtain the yield strength of the metal pipe fitting through the tensile test of the metal pipe fitting ; (2) Obtain the stress-strain curves of multiple metal pipe fittings through Gleeble tests, and obtain the flow stress model of the metal pipe fittings based on the stress-strain curves of the multiple metal pipe fittings; (3) Obtain the processing deformation temperature T, the drawing outlet linear velocity of the metal pipe fitting , the wall thickness of the finished pipe , the outer diameter of the finished pipe , the wall thickness of the incoming metal pipe fitting , the friction coefficient between the metal pipe fitting and the inner hole wall of the die and the friction coefficient between the metal pipe fitting and the mandrel ; (4)A preset fixed mandrel cone die is used to draw the incoming metal pipe fitting to obtain a finished pipe. The deformation zone of the metal pipe fitting during the drawing process is divided into a diameter reduction zone and a wall thickness reduction zone. Based on the rheological stress model of the metal pipe fitting described in step (2), the parameters obtained in step (3), and the calculation formula in the energy method, the outer diameter of the incoming metal pipe fitting and the compression angle of the drawing hole are used as variables to iteratively calculate the average drawing stress at the outlet end face of the drawn pipe fitting . The condition for terminating the iterative calculation is: Wherein, is the error value; after terminating the calculation, the and corresponding to the design are obtained; The calculation formula in the energy method includes the following calculation formula: In the formula, The work done by the drawing force at the drawing exit corresponding to the unit volume, and its calculation formula is as follows: In the formula, is the average drawing stress of the outlet end face of the drawn pipe fitting; For the metal flow occurring during drawing The length of the corresponding pipe fitting after drawing; During drawing, there is metal flow The length of the corresponding pipe fitting before drawing; is the ideal unit volume strain energy of the diameter reduction zone, and its calculation formula is: In the formula, is the average flow stress corresponding to the diameter reduction deformation zone; is the equivalent strain value that occurs in the metal pipe fitting within the reducing deformation zone, and its calculation formula is: In the formula, Substitute the above-mentioned into the flow stress model of the metal pipe fitting described in step (2) to calculate the average flow stress in the drawing and reducing diameter zone , and in the calculation process, the approximate value calculation formula of the equivalent strain degree is: Equivalent strain rate The calculation formula is as follows: In the formula, t is the deformation time for the metal to pass through the deformation zone, and its calculation formula is: In the formula, is the inlet linear velocity of the metal pipe fitting; is the instantaneous linear velocity at the entrance of the metal pipe fitting into the wall thickness reduction zone; and The value of is calculated based on the law of constant metal volume on the premise of the known drawing outlet linear velocity of the metal pipe fitting; is the ideal unit volume strain energy of the wall-thinning region, and its calculation formula is: In the formula, is the average flow stress corresponding to the wall-thinning deformation zone; is the equivalent strain value occurring in the pipe fitting within the wall thickness reduction deformation zone, and its calculation formula is: In the formula, Substitute the above-mentioned into the flow stress model of the metal pipe fitting described in step (2) to calculate the average flow stress in the drawing and wall thickness reduction zone ; During the calculation process, the approximate value calculation formula for the equivalent strain degree is as follows: Equivalent strain rate The calculation formula is as follows: In the formula, t is the deformation time for the metal to pass through the deformation zone, and its calculation formula is: In the formula, is the drawing outlet linear velocity of the metal pipe fitting, is the instantaneous linear velocity when the metal pipe fitting enters the wall thickness reduction area, , The value of is calculated based on the law of constant metal volume on the premise of the known drawing outlet linear velocity of the metal pipe fitting; is the shear strain energy per unit volume in the deformation zone, and its calculation formula is as follows: In the formula, is the compression angle of the drawing hole; The work done by friction per unit volume in the deformation zone, and its calculation formula is as follows: In the formula, is the friction coefficient between the metal pipe fitting and the inner hole wall of the mold; is the friction coefficient between the metal pipe fitting and the mandrel; is the radial component of the pressure of the die in the diameter-reducing area on the metal pipe fitting; is the radial component of the pressure of the die in the wall-thinning area on the metal pipe fitting; is the pressure of the mandrel on the inner wall of the metal pipe fitting in the wall-thinning area; The work done by the metal per unit volume flow rate to overcome friction in the reducing zone; The length of the work done by the metal with a unit volume flow rate to overcome friction in the wall thickness reduction zone.

2. The design method of drawing metal pipe fittings based on a fixed mandrel conical die according to claim 1, characterized in that, During the tensile test process, set multiple tensile pause points so that the yield strength of the metal pipe fitting is the yield strength of the metal pipe fitting with the cumulative work hardening effect.

3. The design method of a metal pipe fitting based on drawing with a fixed mandrel conical die according to claim 1, characterized in that In step (2), the flow stress model of the metal pipe fitting is the Johnson-Cook flow stress model.

4. The design method of a metal pipe fitting based on drawing with a fixed mandrel conical die according to claim 1, wherein In step (3), the is 0.5 - 4 mm.

5. The design method of drawing metal pipe fittings based on a fixed mandrel conical die according to claim 1, characterized in that In step (3), the is 20 - 40 mm.

6. The design method of drawing metal pipe fittings based on a fixed mandrel conical die according to claim 1, characterized in that, In step (3), the is 0.5 - 4 mm.

7. The design method of drawing metal pipe fittings based on a fixed mandrel conical die according to claim 1, characterized in that In step (3), the is 400 - 800 mm / s; in step (3), the is 15 - 30 °C.

8. The design method of drawing metal pipe fittings based on a fixed mandrel conical die according to claim 1, characterized in that, In step (4), the is 30 - 80 mm.

9. The design method of drawing metal pipe fittings based on a fixed mandrel conical die according to claim 1, characterized in that, In step (4), the is 8 - 20°.

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